I. Technical Field
The present disclosure relates to enhancing coverage in a wireless network and in particular relates to apparatuses and methods for providing scheduling order of downlink control information (DCI) in a wireless network.
II. Background
From Global System for Mobile Communications/General Packet Radio Service (GSM/GPRS) to Long Term Evolution (LTE), cellular networks have evolved to support higher data rates and wider coverage. At the same time, the evolution has brought about technical challenges, including, for example, support for high complexity as well as low complexity devices, and cost of overall network maintenance with a large number of radio access technologies (RATs) as evolved network deployments, for example LTE, may require.
With respect to supporting low cost and low complexity devices, Machine-Type Communications (MTC) has been considered as a market likely to expand in the future. MTC is a form of data communication which involves one or more entities that do not necessarily need human interaction. A service optimized for machine type communications differs from a service optimized for Human to Human communications. MTC is different to current mobile network communication services as it involves different market scenarios. Distinctive MTC features may include low mobility, small data transmissions, infrequent termination originated by MTC User Equipment (UE), group based policing and group based addressing. These MTC features derive to low cost and low complexity MTC UEs. MTC UE is a user equipment supporting MTC capabilities in present application. As an example, MTC UE may be a vending machine, a water meter, a gas meter, etc.
It is envisaged that MTC UEs will be deployed in huge numbers, large enough to create an eco-system on its own. MTC UEs used for many applications will require low operational power consumption and are expected to communicate with infrequent small burst transmissions. Some operators see MTC via cellular networks as a significant opportunity for new revenues, because the operators can efficiently serve MTC UE using already deployed RAT.
In addition, there is a substantial market for MTC UEs deployed inside buildings. For example, some MTC UEs are installed in the basements of residential buildings or locations shielded by foil-backed insulation, metalized windows, or traditional thick-walled building construction, and would experience significantly greater penetration losses on the radio interface than normal LTE devices. The MTC UEs in the extreme coverage scenario might have characteristics such as very low data rate, greater delay tolerance, and no mobility, and therefore some messages/channels may not be required. It is necessary to find a solution to support low-end MTC UEs in LTE system.
3rd Generation Partnership Project (3GPP) has studied to find a solution. It was concluded in 3GPP TR 36.888 that a target coverage improvement of 15-20 dB for both Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD) in comparison to normal LTE footprint could be achieved to support MTC devices deployed in challenging locations, e.g., deep inside buildings, and to compensate for gain loss caused by complexity reduction techniques. It was also concluded in 3GPP TR 36.888 that, in order to increase coverage of LTE system, data or control subframes must be repeated multiple times, and a number of repetition between 42 and 400 have been disclosed in section 9.5.6.1 for Physical Downlink Shared CHannel (PDSCH).
It has further been assumed that downlink data transmission can take place on different frequencies than downlink control. Associated control and data are time multiplexed. The time multiplexing and repetition of the downlink control and data subframes create a scheduling problem because all downlink control subframes should be received before starting the actual data reception or at least the repetition factor should be taken into account when determining timing for the transmission of data subframes. It may be possible for UE to be able to receive downlink control correctly without receiving all the repetitions but since that cannot be known by an evolved node B (eNB) the transmission of downlink data can start only after all control repetitions have been transmitted. Furthermore, UE should be able to receive multiple downlink control messages in order to use the system efficiently. For example, there may be a need for simultaneous uplink and downlink data grants. In LTE system data, transmissions both in downlink and uplink are always granted by the eNB by using downlink control channel. The grant contains information on frequency and time resources of the data channel and possibly information on the transmission format such as modulation and channel coding rate.
The current LTE system has multiple DCI formats for downlink control information on Physical Downlink Control CHannel (PDCCH) or Enhanced-PDCCH (E-PDCCH), 3GPP TS 36.212 describes a plurality of DCI formats. For example, DCI format 0 is used for scheduling of PUSCH in one uplink cell. DCI format 1 is used for scheduling of one PDSCH codeword in one cell, and DCI format 1A is used for the compact scheduling of one PDSCH codeword in one cell and random access procedure initiated by a PDCCH order. DCI format 2 is used for transmitting carrier indicator, downlink scheduling information, and so on. DCI format 2A carries carrier indicator, resource allocation header, resource block assignment, precoding information, etc. DCI format 2B carries scrambling identity, downlink assignment index, carrier indicator, resource allocation header, resource block assignment, etc. DCI format 3 and 3A are used for the transmission of TPC commands for PUCCH and PUSCH with 2-bit power adjustments, DCI format 4 is used for scheduling of PUSCH in one uplink cell with multi-antenna port transmission mode.
A UE may need to receive multiple DCIs in a single subframe. In current LTE frame structure both PDCCH and E-PDCCH are located completely in the same subframe as the associated PDSCH data, as shown in FIG. 6. In prior art frame structure 600, both PDCCH 660 and E-PDCCH 630 and 640 are located in the same subframe 620 as associated PDSCH 650, as current LTE systems provide. That is, a LTE 110 may be configured to receive all downlink control channels as well as downlink shared channel in the same subframe 620 over a system bandwidth 610.
A legacy UE can receive all the data in the current system since the whole system bandwidth is received by the UE all the time. For example, a legacy UE supporting LTE Release 12 with MTC features can receive the whole system bandwidth. The legacy UE, however, does not support repetitions and hence can receive control information over PDCCH or E-PDCCH. In other words, a legacy UE, including an MTC capable UE, may be able to receive PDSCH data and possibly downlink control information, such as uplink grant or Physical Hybrid ARQ Indicator CHannel (PHICH) or uplink power control commands, which are transmitted on PDCCH or E-PDCCH. On the other hand, an MTC UE supporting LTE Release 13 and onward releases can receive narrowband only and support repetitions. The MTC UE supporting LTE Release 13 and onwards can thus reuse MTC PDCCH. In the present application, the terminology of MTC UE for invention is directed to a UE which is MTC capable and supports LTE Release 13 and onward releases.
In the present disclosure, unless otherwise specified, PDCCH refers to MTC PDCCH when discussed in context of MTC UE. Compared to the legacy PDCCH, which is transmitted using an entire system bandwidth, MTC PDCCH is transmitted over one narrow band. Therefore, the legacy PDCCH cannot be used for MTC.
3GPP R1-153111, a proposal submitted by Sierra Wireless, proposes simultaneous transmission of uplink and downlink grants for MTC normal coverage case where repetition over multiple subframes is not used. This resembles the current LTE system where any control is transmitted in a subframe and UE can receive all the control. 3GPP document in R1-153111 also assumes that PDCCH and PDSCH can be simultaneously received, which may not be the case if repetition and frequency hopping over narrow bands are used in the enhanced coverage case. R1-153111 further considers that it is more efficient to first exhaust the frequency domain allocation rather than the repetition in time. Hence, repetition is used after the transmission already fills the entire narrow band.
3GPP R1-152601, proposal submitted by Alcatel-Lucent et.al., proposes different timing of different length DCIs in order to reduce simultaneous blind decoding but this proposal does not cover possible need to change a narrow band in MTC. Furthermore, the timing proposal in 3GPP R1-152601 does not specify whether it falls on the assumed search space constraints or not. This proposal introduces a method to reduce complexity by reducing number of simultaneous decoding. Although the proposal discusses the reception of multiple, possibly repeated, DCIs, it does not propose what UE should do after successfully decoding a DCI, for example, whether to continue decoding further DCI candidates or possibly change narrowband which would prevent reception of the rest of the DCIs.
Therefore, the present application intends to provide a solution of scheduling order of DCI to a certain UE such a way that data reception and possible frequency change does not happen before transmission of all DCI is finished.